Recording disk and disk drive

ABSTRACT

Embodiments of the present invention provide a recording disk capable of curtailing the amount of servo data to be stored thereon, and a disk drive. According to one embodiment, servo data area sets each of a first servo data area and plural second servo data areas arranged in that order in a read direction HR are arranged successively on each of tracks of a magnetic disk. Stored in a second sector data section included in the second servo data area is data representing a distance in the read direction HR from the position of the first servo data area to that of the same second servo data area. The amount of data stored in the second sector data section is less than that of data stored in a first sector data section included in the first servo data area.

CROSS-REFERENCE TO RELATED APPLICATION

The instant nonprovisional patent application claims priority toJapanese Patent Application No. 2007-002295 filed Jan. 10, 2007 andwhich is incorporated by reference in its entirety herein for allpurposes.

BACKGROUND OF THE INVENTION

In a disk drive, such as a hard disk drive, a recording disk hascircular tracks formed in its major surface and storing user data andservo data. The servo data is used for controlling the movement of ahead for writing or reading operations. The servo data includes trackdata on the tracks, and sector data identifying sectors in the tracks.

The storage capacity of recording disks has been progressively increasedin recent years. The ratio of the servo data to all the data recorded onthe recording disk has increased as the storage capacity increases.There is a possibility that such increase of the servo data reduces thecapacity for storing user data.

For example, when the width of tracks is reduced to provide a recordingdisk of a large storage capacity, head positioning accuracy needs to beincreased. Therefore, the number of servo data areas in the tracks isincreased and sampling frequency at which servo data is sampled isincreased. Consequently, bit length for sector data increases and servodata increases.

When the number of tracks is increased to increase the storage capacityof the recording disk, bit length necessary for track data and servodata increase.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide a recording disk capable ofcurtailing the amount of servo data to be stored thereon, and a diskdrive. According to the particular embodiment of FIG. 1, servo data areasets each of a first servo data area 10 and plural second servo dataareas 20 arranged in that order in a read direction HR are arrangedsuccessively on each of tracks 2 of a magnetic disk 1. Stored in asecond sector data section included in the second servo data area 20 isdata representing a distance in the read direction HR from the positionof the first servo data area 10 to that of the same second servo dataarea 20. The amount of data stored in the second sector data section isless than that of data stored in a first sector data section included inthe first servo data area 10.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of assistance in explaining the structure ofa magnetic disk.

FIGS. 2(A) and 2(B) are diagrammatic views showing first servo dataareas and second servo data areas in the magnetic disk by way ofexample.

FIG. 3 is a diagrammatic view showing the contents of the first and thesecond servo data areas in the magnetic disk by way of example.

FIG. 4 is a block diagram of a magnetic disk drive.

FIG. 5 is a block diagram of an essential part of the magnetic diskdrive.

FIG. 6 is a low chart of a seek control procedure to be executed by themagnetic disk drive.

FIG. 7 is a flow chart of a magnetic head positioning control procedureto be executed by the magnetic disk drive.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention relate to a recording disk storingservo data and a disk drive using the recording disk.

Embodiments of the present invention have been made under the foregoingcircumstances and it is an object of the present invention to provide arecording disk capable of curtailing the amount of servo data to berecorded thereon, and a disk drive.

Embodiments of the present invention provide a recording disk havingfirst and second servo areas arranged along tracks; wherein each of thefirst servo data areas includes a first sector data part indicating theposition of the first servo data area in the track, and each of thesecond servo data areas includes a second sector data part indicatingthe position of the second servo data area with respect to the positionof the first servo data area and storing a less amount of data than thefirst sector data part.

In the recording disk according to embodiments of the present invention,the first servo data area includes a first track data part identifyingthe track among all the tracks, and the second servo data area includesa second track data part identifying the track among the adjacent tracksand storing a less amount of data than the first track data part.

A disk drive according to embodiments of the present invention includes:the recording disk of the present invention; a head for reading servodata from the recording disk; an actuator for moving the head relativeto the recording disk; and a position control circuit for indicating thepresent position of the head on the basis of servo data read by the readhead, and driving the actuator on the basis of a positional errorbetween a desired position of the read head and the present position ofthe read head; wherein the position control circuit indicates a positionof the head on the track on the basis of the servo data read from thefirst servo data area, and then indicates the position of the head onthe track by indicating the position of the head with respect to theindicated position on the basis of the servo data read from the secondservo data area.

In the disk drive according to embodiments of the present invention, theposition control circuit includes a sector counter for counting thenumber of cycles of an operation performed for reading servo data fromthe second servo data area after the servo data has been read from thefirst servo data area.

In the disk drive according to embodiments of the present invention,data representing order of the second servo data areas arranged in adirection in which the data reading operation of the head proceeds withrespect to the first servo data area is recorded in the second sectordata part included in the second servo data area, and the positioncontrol circuit compares the order of the second servo data read fromthe second servo data area and the number of cycles of an operation forreading data from the second servo data areas counted by the counter tosee whether or not the order of the second servo data and the number ofcycles of the operation coincide with each other.

The disk drive according to embodiments of the present inventionincludes the recording disk, the position control circuit indicates thepresent position of the head by acquiring only the servo data from thefirst servo data area when a position to which the head is to be movedwith respect to the present position of the read head is outside anadjacent track range covering the adjacent tracks, and the positioncontrol circuit indicates the present position of the head by acquiringthe servo data from the first and the second servo data area when aposition to which the read head is to be moved is within the adjacenttrack range.

Embodiments of the present invention curtail the amount of servo data tobe recorded on the recording disk.

Certain embodiments of the present invention will be described withreference to the accompanying drawings.

A disk drive in a preferred embodiment according to the presentinvention is a magnetic disk drive, such as a hard disk drive. Theembodiments of present invention are applicable to other disk drivesemploying a recording disk storing servo data.

FIG. 1 is a view of assistance in explaining the structure of a track ona magnetic disk 1. The magnetic disk 1 is a disk having a major surfaceon which data is recorded magnetically. The magnetic disk 1 isincorporated into a magnetic disk drive, which will be described later.A magnetic head moves above the major surface of the magnetic disk 1 towrite data to or read data from the magnetic disk 1. The magnetic disk 1is rotated during writing data to and reading data from the magneticdisk 1. A direction in which the magnetic head is moved to read datafrom the magnetic disk, namely, a read direction HR, is opposite arotating direction DR in which the magnetic disk 1 rotates.

Plural tracks 2 are formed concentrically about the center of themagnetic disk 1 on the major surface of the magnetic disk 1. Only one ofthe tracks 2 is shown in FIG. 1.

The track 2 has user data areas 30 for storing user data, and servo dataareas for storing servo data. The user data areas 30 and the servo dataareas are arranged alternately along the track 2. The servo data areasinclude two types of servo data areas, namely, first servo data areas 10and second servo data areas 20.

The plural second servo data areas 20 are disposed between the twoadjacent first servo data areas 10 on the track 2. That is, servo dataarea sets each of the one first servo data area 10 and the plural secondservo data areas 20 arranged in that order in the read direction HR arearranged successively in the read direction HR.

In this embodiment, in each servo data area set, the two second servodata areas 20 precede the first servo data area 10 with respect to theread direction HR. The number of the second servo data areas 20 in eachservo data area set is not limited to two.

FIG. 2(A) shows the structure of the first servo data area 10 by way ofexample, and FIG. 2(B) shows the structure of the second servo data area20 by way of example.

As shown in FIG. 2(A), the first servo data area 10 has a gain controldata section (AGC) 11, a first servo mark section 12, a first track datasection 13, a first sector data section 14, and a burst section 15arranged in that order in the read direction HR.

The gain control data section 11 stores a signal for making the magneticdisk drive adjust the amplification factor of a head amplifier. Theburst section 15 stores a signal for making the magnetic disk drivegrasp the position of the magnetic head relative to the track.

The first servo mark section 12 stores first mark data indicating thefirst servo data area 10.

The first track data section 13 stores first track data indicating thetrack on which the first servo data area 10 is included among all theradially arranged tracks. The first track data indicates a track numberpeculiar to the track. The first track data can specify a position onthe magnetic disk 1 with respect to a radial direction.

The first sector data section 14 stores first sector data indicating thepositions of the first servo data areas 10 in the track. The firstsector data indicates sector numbers assigned to sectors in ascendingorder in the read direction HR. The first sector data directly specifiesthe circumferential positions of the magnetic disk 1.

As shown in FIG. 2(B), the second servo data area 20 has a gain controldata section (AGC) 21, a second servo mark section 22, a second trackdata section 23, a second sector data section 24, and a burst section 25arranged in that order in the read direction HR.

The gain control data section 21, similarly to the gain control datasection 11, stores a signal for making the magnetic disk drive adjustthe amplification factor of the head amplifier. The burst section 25,similarly to the burst section 15, stores a signal for making themagnetic disk drive grip the position of the magnetic head relative tothe track.

The second servo mark section 22 stores second mark data indicating thesecond servo data areas 20. The bit length of the second servo marksection 22 is equal to that of the first servo mark section 12.

The second track data section 23 stores second track data indicating thetrack on which the second servo data areas 20 are included among theadjacent tracks. The second track data identifies the relevant trackamong the adjacent tracks by a track number of a bit length shorter thanthat of the track number represented by the first track data.

In this embodiment, the second track data represents the lower bits ofpredetermined digit positions in the track number represented by thefirst track data. Thus the relevant track among the number representedby the lower bits of the adjacent tracks can be identified. For example,if the lower bits are eight digit positions, the relevant track among256 (28) tracks equally distributed on the opposite sides around thefirst track data the relevant track can be identified. Hereinafter, arange covering those adjacent tracks will be referred to as “adjacenttrack range”.

When the magnetic disk drive operates for positioning the magnetic heador a seek operation for moving the magnetic head such that magnetic headis moved for a moving distance within the adjacent track range, thesecond track data can indicate a position with respect to a radialdirection on the magnetic disk 1.

The second sector data section 24 stores second sector data indicatingthe positions of the second servo data areas 20 with respect to thepositions of the first servo data sections 10. The second sector dataindicates distances of the positions of the second servo data areas 20in the read direction HR from the first servo data area 10 by numbers ofa bit length shorter than that of the sector number indicated by thefirst sector data. More concretely, the second servo data representsnumbers indicating order of the second servo data areas 20 arranged inthe read direction HR with respect to the first servo data area 10.

Since the distances of the positions of the second servo data areas 20in the read direction HR from the position of the first servo data area10 can be determined from the second sector data, the circumferentialpositions of the second servo data areas 20 on the magnetic disk 1 canbe indirectly determined by determining the circumferential position ofthe first servo data area 10 on the magnetic disk 1 from the firstsector data stored in the first servo data area 10.

FIG. 3 is a view of assistance in explaining, by way of example, thecontents of the first sector data stored in the first servo data areas10 and the second sector data stored in the second servo data areas 20.

The first sector data stored in the first servo data areas 10 representsserial sector numbers of sectors arranged in the read direction HR. Thesector numbers represented by the first sector data represent the numberof the servo data areas arranged in the read direction HR in the track2. For example, the interval between adjacent one of numbers 121, 124,127 and such is equal to the number of the second servo data areas 20between the successive first servo data areas 10. In this embodiment,the two first servo data areas 20 are arranged between the twosuccessive first servo data areas 10. A circumferential position on themagnetic disk 1 can be specified by the sector number represented by thefirst sector data.

The second sector data stored in the second servo data areas 20represents serial numbers, such as 1 and 2, of the second servo areas 20arranged in that order in the read direction HR with respect to thefirst servo data area 10. Therefore, the circumferential position of thesecond servo data area 20 on the magnetic disk 1 can be specified by anumber, such as a sector number 126, obtained by adding a sector number,such as sector number 2, represented by the second sector data to asector number, such as sector number 124, represented by the firstsector data stored in the first servo data area 10 immediately beforethe second servo data area 20.

Thus, in the magnetic disk 1, the second servo data area 20 includes thesecond track data section 23 and the second sector data section 24storing amounts of data smaller than those of data stored in the firsttrack data section 13 and the first sector data section 14 of the firstservo data area 10. Consequently, increase in the ratio of the servodata to all the data stored in the magnetic disk 1 can be prevented.

FIG. 4 is a block diagram of a magnetic disk drive. In the magnetic diskdrive, the foregoing magnetic disk 1, a spindle motor 41, a magnetichead 42, a suspension arm 43, a voice coil motor 44, namely, anactuator, and a head amplifier 45 are held in a case 48.

The magnetic disk drive includes a main circuit 50, namely, a positioncontrol circuit, a buffer memory 58, and a motor drive 57 disposedoutside the case 48. The main circuit 50 includes a microprocessor unit(MPU) 51, a memory 52, a hard disk controller (HDC) 53, and a read/writechannel (R/W channel) 54.

The magnetic disk 1 is mounted on and driven for rotation by the spindlemotor 41. The magnetic head 42 writes data magnetically to and readsdata magnetically from the magnetic disk 1. The magnetic head 42 is heldon the tip of the suspension arm 43. The suspension arm 43 is turned ona pivot by the voice coil motor 44 to move the magnetic head 42 held onthe tip of the suspension arm 43 above the magnetic disk 1 substantiallyalong a radius of the magnetic disk 1.

The MPU 51 controls all the operations of the magnetic disk drive. Uponthe reception of a write or read command sent out from a host devicefrom the HDC 53, the MPU 51 controls the voice coil motor 44 accordingto the command to move the magnetic head 42 to a position correspondingto a desired track on the magnetic disk 1 for writing or readingoperations.

The MPU 51 determines the present position of the magnetic head 42 onthe basis of servo data received from the HDC 53 and obtains a positionerror signal (PES) representing the difference between a desiredposition of the magnetic head 42 described in the write or read commandand the present position of the same. Then, the MPU 51 generates a drivesignal for driving the voice coil motor 44 from the position errorsignal, and gives the drive signal to the motor driver 58.

The MPU 51 executes a seek control operation for moving the magnetichead 42 to a position corresponding to the desired track and apositioning operation for positioning the magnetic head 42 at theposition corresponding to the desired track to move the magnetic head 42to the position corresponding to the desired track. Those operationswill be described later.

The memory 52 includes a flash memory and a RAM (random-access memory).The flash memory stores programs to be carried out by the MPU 51. TheRAM serves as a work memory for the MPU 51.

Upon the reception of the drive signal for driving the voice coil motor44 from the MPU 51, the motor driver 58 converts the drive signal intoan analog drive signal, amplifies the analog drive signal and gives theamplified analog drive signal to the voice coil motor 44. Upon thereception of a drive signal for driving the spindle motor 41 from theMPU 51, the motor driver 58 converts the drive signal into an analogdrive signal, amplifies the analog drive signal and gives the amplifiedanalog drive signal to the spindle motor 41.

The HDC 53 includes an interface controller, an error correctingcircuit, a buffer controller and a servo controller.

Upon the reception of data to be written to the magnetic disk 1, namely,write data, from the external host device, the HDC 53 sends out thewrite data to the R/W channel 54. Upon the reception of data read fromthe magnetic disk 1, namely, read data, from the R/W channel 54, the HDC53 sends the read data to the external host device. The HDC 53 iscontrolled by the MPU 51 so as to hold the write data and the read datatemporarily in the buffer memory 57.

Upon the reception of a write or read command from the host device, theHDC 53 sends the write or read command to the MPU 51. The HDC 53 sendsservo data acquired from the R/W channel 54 to the MPU 51. Theacquirement of the servo data will be described later.

Upon the reception of the write data from the HDC 53, the R/W channel 54modulates the write data, converts the modulated write data into ananalog signal and gives the analog signal to the head amplifier 45. Whena signal read from the magnetic disk 1 is given to the R/W channel 54 bythe head amplifier 45, the R/W channel 54 converts the signal intodigital data, demodulates the digital data and gives the demodulatedsignal to the HDC 53.

The R/W channel 54 samples servo data from the read data at apredetermined sampling period and gives the servo data to the HDC 53.Sampling the servo data will be described later.

Upon the reception of a write signal to be written to the magnetic disk1 from the R/W channel 54, the head amplifier 45 amplifies the writesignal and gives the amplified write signal to the magnetic head 42.Upon the reception of a read signal read from the magnetic disk 1 fromthe magnetic head 42, the head amplifier 45 amplifies the read signaland gives the amplified read signal to the R/W channel 54.

FIG. 5 is a view of assistance in explaining the HDC 53 and the R/Wchannel 54. The R/W channel 54 gives the user data included in the readdata to the HDC 53. The HDC 3 gives the write data to the R/W channel54.

The R/W channel 54 has a position information sampler 61 for samplingservo data from the read data. The position information sampler 61samples servo data from the read data when the HDC 53 asserts a servogate 83 in a predetermined timing, and gives the sampled servo data tothe HDC 53. The operation of the HDC 53 for timing asserting the servogate 83 determines the sampling period at which the servo data issampled.

The position information sampler 61 is capable of discriminating firstmark data included in first servo data, and second mark data included inthe second servo data from each other. In a state where a first servoacquisition gate 84 is asserted by the HDC 53, the first servo data issampled from the read data. In a state where the first servo acquisitiongate 84 is negated by the HDC 53, the second servo data is sampled fromthe read data.

More concretely, when the HDC 53 asserts the servo gate 83 and the firstservo acquisition gate 84 is asserted, the position information sampler61 detects the first mark data, samples the first track data and thefirst sector data following the first mark data and sends the sampleddata to the HDC 53. When the HDC 53 asserts the servo gate 83 andnegates the first servo acquisition gate 84, the position informationsampler 61 detects the second mark data, samples the second track dataand the second sector data following the second mark data, and gives thesampled data to the HDC 53.

As shown in FIGS. 1 and 3, in the magnetic disk 1 in this embodiment,the plural sets each of the first servo data area 10 and the pluralsecond servo data areas 20 arranged in that order in the read directionHR are arranged successively in the read direction HR. Therefore, theHDC 53 times asserting servo gate 83 and the first servo acquisitiongate 84 to obtain the first servo data and the second servo data fromthe data read from the magnetic disk 1.

Thus the HDC asserts the servo gate 83 at times when the servo dataappears in the read data, asserts the first servo acquisition gate 84 attimes when the first servo data appears, and negates the first servoacquisition gate 84 at ties when the second servo data appears. Forexample, when a first servo data area 10 and M second servo data areas20 are arranged in that order in the read direction HR on the magneticdisk 1 an assertion period at which the first servo acquisition gate 84is asserted is M+1 times a sampling period at which the servo gate 83 isasserted.

The MPU 51 receives the thus acquired first sector data and the secondsector data from the HDC 53, and determines the position of the magnetichead 42 relative to the magnetic disk 1 on the basis of the receiveddata. A circumferential position on the magnetic disk 1 is directlyspecified by using a sector number represented by the first sector data,and a circumferential position on the magnetic disk 1 is indirectlyspecified by using a number obtained by adding a number represented bythe second sector data following the first sector data to the sectornumber represented by the precedent first sector data.

In this magnetic disk drive, the first sector data is acquired firstfrom the read data read from the magnetic disk 1, and then a position ona track corresponding to the magnetic head 42 is determined on the basisof the first servo data. Subsequently, the second servo data isacquired, the distance between the position specified by the first servodata on the track and a position corresponding to the magnetic head 42is determined on the basis of the second servo data to determine theposition of the magnetic head 42 relative to the magnetic disk 1. Themagnetic disk drive also acquires the first sector data first, forexample, in a case where the position of the magnetic head 42 relativeto the magnetic disk 1 is specified for the first time after themagnetic disk drive 1 has been connected to a power supply.

To acquire only the first servo data from the read data read from themagnetic disk 1, the HDC 53 asserts the servo gate 83 at the time thefirst servo data appears in the read data and asserts the first servoacquisition gate 84 at the same time. For example, when a first servodata area 10 and M second servo data areas 20 are arranged in that orderin the read direction HR on the magnetic disk, a sampling period atwhich the second servo gage 83 is asserted is M+1 times a samplingperiod at which both first and the second servo data are acquired. Onlythe first servo data can be acquired from the read data by asserting thefirst servo acquisition gate 84 at that period.

The HDC 53 has an index counter 71 for counting the number of theacquired servo data, and a sector counter 72 for counting the number ofthe acquired second servo data.

The index counter 71 is set to a sector number represented by the firstsector data when the first servo data is acquired. The sector number isincremented by one every time the second servo data is acquired. Thusthe position on the track corresponding to the magnetic head 42 can bealso specified by the index counter 71. A number counted by the indexcounter 71 is used for deciding whether or not the servo data has beenproperly acquired, which will be described later.

The sector counter 72 is set to an initial value 0 when the first servodata is acquired. The number counted by the sector counter 72 isincremented by one every time the second servo data is acquired. Thusthe distance between the current position of the magnetic head 42 and aposition corresponding to a position on the track specified by the firstservo data can be specified by the number counted by the sector counter72. The number counted by the sector counter 72 is used for examiningwhether or not the servo data is properly acquired, which will bedescribed later.

A description will be made of a seek control procedure and a magnetichead positioning control procedure to be executed by the MPU 51 to movethe magnetic head 42 to a position corresponding to a desired track ofthe magnetic disk 1.

FIG. 6 is a flow chart of the seek control procedure for moving themagnetic head 42 to a position corresponding to a desired track. Firstthe MPU 51 decides in step S11 whether or not a desired track at whichthe magnetic head 42 is to be positioned described in a write or readcommand received from the external host device is within an adjacenttrack range equally extended on the opposite sides of a trackcorresponding to around the present position of the magnetic head 42.

The relevant track in the adjacent track range can be identified by thesecond track data represented by the lower bits of predetermined digitpositions in the first track data. For example, when the second trackdata is represented by lower bits of N digit positions, the adjacenttrack range covers 2N−1 tracks on each of the inner and the outer sideof the track corresponding to the present position of the magnetic head.

If it the response to the query made in step S11 is affirmative, namely,the track corresponding to the desired position of the magnetic head 42is not within the adjacent track range, the MPU 51 controls the HDC 53so as to acquire only the first servo data from the read data,determines the present position of the magnetic head 42 on the basis ofthe first servo data, and moves the magnetic head 42 for a seekoperation on the basis of the present position in step S12. As mentionedabove, only the first servo data can be acquired by changing thesampling period at which the HDC 53 samples the servo data.

After the seek operation has been started, the MPU 51 performspredetermined operations including a speed reducing operation which isstarted upon the arrival of the magnetic head 42 at about the middlepoint of a seek length. When the track corresponding to the desiredposition of the magnetic head 42 is within the adjacent track range,i.e., if the response to the query made in step S13 is affirmative, theMPU 51 controls the HDC 53 so as to acquire both the first and thesecond servo data from the read data, determines the present position ofthe magnetic head 42 on the basis of those servo data, and controls themagnetic head 42 for a seek operation on the basis of the presentposition (Step S14).

Upon the arrival of the magnetic head 42 at a desired positioncorresponding to the desired track, the MPU 51 executes a magnetic headpositioning control operation to position the magnetic head at thedesired position corresponding to the desired track.

The magnetic disk drive can move the magnetic head 42 for the seekoperation over the entire radial range on the magnetic disk 1 storingthe first and the second track data.

Although this embodiment decides whether or not the desired trackcorresponding to the desired position of the magnetic head 42 is withinthe adjacent track range, a decision may be made as to whether or not amoving rate at which the magnetic head 42 is moved for the seekoperation exceeds the adjacent track range equally extended on theopposite sides of a track corresponding to around the present positionof the magnetic head 42.

FIG. 7 is a flow chart of the magnetic head positioning controlprocedure for positioning the magnetic head 42 at a positioncorresponding to the desired track. Upon the arrival of the magnetichead 42 at the position corresponding to the desired track, the MPU 51starts the magnetic head positioning control procedure to write or readuser data.

The MPU 51 acquires the first servo data from the HDC 53 in step S21.Then, the MPU 51 compares a sector number represented by the firstsector data included in the first servo data and a number counted by theindex counter 71 in step S22. If those numbers are equal to each other,i.e., if the response to a query made in step S22 is affirmative, theMPU 51 sets the index counter 71 to a sector number represented by thefirst sector data included in the first servo data in step S24 and setsthe sector counter 72 to the initial value of 0 in step S25. Then, theMPU 51 sets the HDC 53 in a second servo data acquisition mode in stepS26. Those steps are achieved by making the HDC 53 negate the firstservo acquisition gate 84 as mentioned above in connection with FIG. 5.

If the sector number represented by the first sector data does notcoincide with the number counted by the index counter 71, i.e., if theresponse to the query made in step S22 is negative, the operation forwriting or reading the user data is stopped in step S23.

The index counter 71 is set to a sector number represented by the firstsector data acquired in the preceding sampling cycle and the number isincremented by one every time the second servo data is acquired.Therefore, the number counted by the index counter 71 should coincidewith a sector number represented by the first sector data acquired inthe succeeding sampling cycle when those servo data are acquiredproperly. Thus, when the number counted by the index counter 71 does notcoincide with the sector number represented by the first sector data, itis decided that the servo data are not properly acquired and the writeor the read operation is stopped.

Upon the reception of the second servo data from the HDC 53 in step S27,the MPU 51 increments the numbers counted respectively by the indexcounter 71 and the sector counter 72 by one in step S28 and step S29. Instep S30, the MPU 51 makes a query to see whether or not a numberrepresented by the second sector data included in the second servo datais equal to the number counted by the second counter 72. If the responseto the query made in step S30 is affirmative, operations for acquiringthose second servo data and the associated operations until apredetermined number of second servo data are acquired while theresponse to a query made in step S32 is negative.

The predetermined number corresponds to the number of second servo datathat appears in a period between the appearance of the preceding firstservo data and that of the succeeding first servo data, and is dependenton the number of the second servo data areas 20 between the adjacentfirst servo areas 10 (FIGS. 1 and 3).

After the MPU 51 has acquired the predetermined number of second servodata, i.e., if the response to a query made in step S32 is affirmative,the HDC 53 is set in a first servo data acquisition mode in step S33,and the procedure returns to step S21 to repeat the first servo dataacquiring steps. This is achieved by making the HDC 53 assert thefirst-servo acquisition gate 84 (FIG. 5).

On the other hand, if the response to the query made in step S30 isnegative, i.e., if the number represented by the second sector dataincluded in the second servo data and the value counted by the sectorcounter 72 do not coincide with each other, operations for writing orreading user data is stopped in step S31.

The number counted by the sector counter 72 is cleared upon theacquisition of the first servo data and is incremented by one every timethe second servo data is acquired. Therefore, a number represented bythe acquired second sector data should coincide with the number countedby the sector counter 72 if those servo data are acquired properly. Ifthe number and the value counted by the sector counter 72 do notcoincide with each other, operations for writing or reading user data isstopped.

The magnetic disk drive can grasp the position of the magnetic head 42even if the magnetic disk 1 stores the first sector data and the secondsector data through the foregoing operation.

1. A recording disk having first and second servo areas arranged alongtracks, wherein each of the first servo data areas includes a firstsector data part indicating the position of the first servo data area inthe track, and each of the second servo data areas includes a secondsector data part indicating a distance in a read direction from theposition of the second servo data area to the position of the firstservo data area and a burst section indicating a position in the trackand storing a less amount of data than the first sector data part. 2.The recording disk according to claim 1, wherein the first servo dataarea includes a first track data part identifying the track among allthe tracks, and the second servo data area includes a second track datapart identifying the track among the adjacent tracks and storing a lessamount of data than the first track data part.
 3. A disk drivecomprising: a recording disk having first and second servo areasarranged along tracks, wherein each of the first servo data areasincludes a first sector data part indicating the position of the firstservo data area in the track, and each of the second servo data areasincludes a second sector data part indicating a distance in a readdirection from the position of the second servo data area to theposition of the first servo data area and a burst section indicating aposition in the track and storing a less amount of data than the firstsector data part; a head for reading servo data from the recording disk;an actuator for moving the head relative to the recording disk; and aposition control circuit for indicating the present position of the headon the basis of servo data read by the read head, and driving theactuator on the basis of a positional error between a desired positionof the read head and the present position of the read head; wherein theposition control circuit indicates a position of the head on the trackon the basis of the servo data read from the first servo data area, andthen indicates the position of the head on the track by indicating theposition of the head with respect to the indicated position on the basisof the servo data read from the second servo data area.
 4. The diskdrive according to claim 3, wherein the position control circuitincludes a sector counter for counting the number of cycles of anoperation performed for reading servo data from the second servo dataarea after the servo data has been read from the first servo data area.5. The disk drive according to claim 4, wherein data representing orderof the second servo data areas arranged in a direction in which the datareading operation of the head proceeds with respect to the first servodata area is recorded in the second sector data part included in thesecond servo data area, and the position control circuit compares theorder of the second servo data read from the second servo data area andthe number of cycles of an operation for reading data from the secondservo data areas counted by the counter to see whether or not the orderof the second servo data and the number of cycles of the operationcoincide with each other.
 6. The disk drive according to claim 4,wherein the position control circuit indicates the present position ofthe head by acquiring only the servo data from the first servo data areawhen a position to which the head is to be moved with respect to thepresent position of the read head is outside an adjacent track rangecovering the adjacent tracks, and the position control circuit indicatesthe present position of the head by acquiring the servo data from thefirst and the second servo data area when a position to which the readhead is to be moved is within the adjacent track range.
 7. The diskdrive according to claim 5, wherein the position control circuitindicates the present position of the head by acquiring only the servodata from the first servo data area when a position to which the head isto be moved with respect to the present position of the read head isoutside an adjacent track range covering the adjacent tracks, and theposition control circuit indicates the present position of the head byacquiring the servo data from the first and the second servo data areawhen a position to which the read head is to be moved is within theadjacent track range.
 8. The disk drive according to claim 3, whereinthe position control circuit indicates the present position of the headby acquiring only the servo data from the first servo data area when aposition to which the head is to be moved with respect to the presentposition of the read head is outside an adjacent track range coveringthe adjacent tracks, and the position control circuit indicates thepresent position of the head by acquiring the servo data from the firstand the second servo data area when a position to which the read head isto be moved is within the adjacent track range.
 9. A disk drivecomprising: a recording disk having first and second servo areasarranged along tracks, wherein each of the first servo data areasincludes a first sector data part indicating the position of the firstservo data area in the track, and each of the second servo data areasincludes a second sector data part indicating a distance in a readdirection from the position of the second servo data area to theposition of the first servo data area and a burst pattern indicating aposition in the track and storing a less amount of data than the firstsector data part; wherein the first servo data area includes a firsttrack data part identifying the track among all the tracks, and thesecond servo data area includes a second track data part identifying thetrack among the adjacent tracks and storing a less amount of data thanthe first track data part; a head for reading servo data from therecording disk; an actuator for moving the head relative to therecording disk; and a position control circuit for indicating thepresent position of the head on the basis of servo data read by the readhead, and driving the actuator on the basis of a positional errorbetween a desired position of the read head and the present position ofthe read head; wherein the position control circuit indicates a positionof the head on the track on the basis of the servo data read from thefirst servo data area, and then indicates the position of the head onthe track by indicating the position of the head with respect to theindicated position on the basis of the servo data read from the secondservo data area.
 10. The disk drive according to claim 9, wherein theposition control circuit includes a sector counter for counting thenumber of cycles of an operation performed for reading servo data fromthe second servo data area after the servo data has been read from thefirst servo data area.
 11. The disk drive according to claim 10, whereindata representing order of the second servo data areas arranged in adirection in which the data reading operation of the head proceeds withrespect to the first servo data area is recorded in the second sectordata part included in the second servo data area, and the positioncontrol circuit compares the order of the second servo data read fromthe second servo data area and the number of cycles of an operation forreading data from the second servo data areas counted by the counter tosee whether or not the order of the second servo data and the number ofcycles of the operation coincide with each other.
 12. The disk driveaccording to claim 10, wherein the position control circuit indicatesthe present position of the head by acquiring only the servo data fromthe first servo data area when a position to which the head is to bemoved with respect to the present position of the read head is outsidean adjacent track range covering the adjacent tracks, and the positioncontrol circuit indicates the present position of the head by acquiringthe servo data from the first and the second servo data area when aposition to which the read head is to be moved is within the adjacenttrack range.
 13. The disk drive according to claim 11, wherein theposition control circuit indicates the present position of the head byacquiring only the servo data from the first servo data area when aposition to which the head is to be moved with respect to the presentposition of the read head is outside an adjacent track range coveringthe adjacent tracks, and the position control circuit indicates thepresent position of the head by acquiring the servo data from the firstand the second servo data area when a position to which the read head isto be moved is within the adjacent track range.
 14. The disk driveaccording to claim 9, wherein the position control circuit indicates thepresent position of the head by acquiring only the servo data from thefirst servo data area when a position to which the head is to be movedwith respect to the present position of the read head is outside anadjacent track range covering the adjacent tracks, and the positioncontrol circuit indicates the present position of the head by acquiringthe servo data from the first and the second servo data area when aposition to which the read head is to be moved is within the adjacenttrack range.